Elastomeric polymers, both homopolymers and copolymers, are well known in the art and include natural rubbers and a wide variety of synthetic materials. A particularly useful class of synthetic elastomers is the class of thermoplastic elastomers which demonstrates elastomeric properties at ambient temperatures but which is processable by methods more conventionally employed for non-elastomeric thermoplastics at somewhat elevated temperatures. Such thermoplastic elastomers are illustrated by block polymers of an alkenyl aromatic compound and a conjugated alkadiene, e.g., a block polymer of styrene and butadiene. This particular type of block polymer is well known in the art and a number are commercial, being marketed by Shell Chemical Company as KRATON.RTM. Thermoplastic Rubber.
It is also well known in the art that certain of the properties of this class of block polymers are improved by the hydrogenation of some or all of the carbon-carbon unsaturation in the polyalkadiene or aliphatic portion and, on some occasions, by hydrogenation of substantially all of the carbon-carbon unsaturation, including that unsaturation in the poly(alkenyl aromatic compound) or aromatic portion. Certain of these hydrogenated or selectively hydrogenated block polymers are also well known and commercial and a number are commercial being marketed as KRATON.RTM.G thermoplastic rubber.
The block polymers of alkenyl aromatic compound and conjugated alkadiene, hydrogenated or non-hydrogenated, are useful for a wide variety of applications and demonstrate a wide range of useful properties. It is, however, desirable on occasion to retain the more beneficial properties of the block polymers while improving certain other properties. One method of property improvement involves the compounding of the thermoplastic elastomers by mixing or blending the elastomers with other materials, organic or inorganic, monomeric or polymeric, which are selected to improve particular properties of the resulting composition without being unduly detrimental toward the properties it is desired to retain. A second method of selective property improvement comprises the functionalization of the thermoplastic elastomer, i.e., the introduction of one or more functional or reactive groups into the molecular structure of the elastomer molecules. Illustrative of such functionalization is the carboxylation of the aromatic portion of the block polymer by reaction with an alkali metal compound, particularly a lithium compound, followed by subsequent reaction of the metallated product with carbon dioxide. Similar reactions take place in the aliphatic portion if the thermoplastic rubber retains ethylenic unsaturation in the aliphatic portion. This process is illustrated by the disclosures of U.S. Pat. No. 4,145,490, U.S. Pat. No. 3,976,628 and published European Patent Application 215,501. Carboxylic acid functions are also introduced into the aliphatic portion by the addition of mercaptoalkanoic acids such as thioglycolic acid to the aliphatic unsaturation or by the grafting of maleic acid compounds such as maleic anhydride onto the aliphatic portion. The former reaction is more fully described by Calhoun et al, U.S. Pat. No. 3,052,657, and the latter reaction by the disclosure of, among many others, U.S. Pat. No. 4,292,414. A copending U.S. patent application Ser. No. 349,547, filed May 9, 1989, describes functionalization of a variety of elastomers by incorporation of carboxylic acid ester groups wherein the ester moiety is a benzocyclobutenealkyl group. Copending U.S. patent application Ser. No. 349,545, filed May 9, 1989, describes other carboxylic acid ester derivatives wherein the ester moiety is propargyl, styrylmethyl or 4-(2-oxazolinyl)benzyl. The salts of primary and secondary amines and carboxylated block polymers, as well as corresponding N-alkylcarboxamides, are disclosed in copending U.S. patent applications Ser. No. 157,348, filed Feb. 17, 1988, and Ser. No. 157,353, filed Feb. 17, 1988. These functionalized derivatives of the thermoplastic elastomers are characterized by modified properties such as improved toughness when compared with the non-functionalized block polymer. Nevertheless, it would be of advantage to provide additional functionalized derivatives of the thermoplastic polymers which additionally demonstrate improved properties.